Intracranial Pressure
B. Sx and progression of herniation
1. Central supratentorial herniation: Usually subacute, from tumor. Diencephalon is forced down through tentorium.
a. Diencephalic stage (reversible): Small pupils with light-near dissociation, roving eyes with decreased upgaze, obtundation, yawning. Progresses to Cheyne-Stokes breathing and decorticate posture.
b. Pontine stage (not reversible): Midsized fixed pupils (even though pontine lesions cause pinpoint nonreactive pupils). Cheyne-Stokes progresses to tachypnea. Decreased doll’s eyes and calorics. Disconjugate gaze ± intranuclear ophthalmoplegia. Decorticate posture becomes decerebrate, then flaccid.
c. Medullary stage: Dilated pupils. Slow, irregular respirations.
2. Uncal supratentorial herniation: Usually rapid, often from hematoma of temporal lobe, malignant cerebral edema following an acute ischemic stroke, encephalitis (e.g., HSV).
a. First stage: Unilateral pupil dilation often before mental status change. Uncal herniation can pinch off PCAs.
b. Second stage: Ophthalmoplegia and hyperventilation. May see Kernohan’s false localizing sign: ipsilateral hemiplegia as contralateral peduncle is compressed.
c. Third stage: Midposition pupils and decerebrate posture.
d. Fourth stage: Sx of central herniation (see *above).
3. Cingulate herniation (subfalcine): Often seen in malignant cerebral edema of ischemic stroke, ICH, GBM. Can pinch off ACA and present with abulia, poor concentration, LE weakness.
4. Subtentorial herniation: Often presents with respiratory arrest, so prophylaxis is more useful than monitoring. Rapid and devastating; often requires emergent neurosurgical intervention (suboccipital decompression).
a. Upward cerebellar herniation: May see dorsal midbrain syndrome.
b. Tonsillar herniation: Compresses medulla.
C. Causes of high ICP
Mechanism determines rx.
1. Mass lesion: E.g., blood, tumor, trauma. Use osmolar agent, mass resection, EVD, VP shunt.
2. Poor CSF resorption: E.g., pseudotumor cerebri (see p. 69). Rx with acetazolamide (decreases CSF production), osmolar agent, shunt.
3. Cerebral edemaRelated posts:
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